1. Technical Field
This application generally relates to a data storage system, and more particularly to techniques used with copying data.
2. Description of Related Art
Host processor systems may store and retrieve data using a storage device containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels of the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical volumes. The logical volumes may or may not correspond to the actual disk drives.
The storage devices may be interconnected to allow for the transfer of data therebetween. In some cases, connection points on the storage devices (“ports”) are shared between hosts and other storage devices so that, for example, a port of a storage device may have both a host and another storage device coupled thereto. However, if a background task related to the interconnection of the storage devices (e.g., a copy between storage devices) uses too much of the data bandwidth of the port, the result may be that host I/O is starved. Accordingly, it is desirable to provide a mechanism to manage port accesses of background I/O tasks and Host I/O tasks.